Stefan G. Kertesz, M.D. is an academic physician in general internal medicine with five years of clinical experience caring for homeless persons addicted to drugs and alcohol, and drug abuse research training experience. As part of his K23 career development award, he will seek to identify factors associated with addiction treatment utilization and addiction outcomes among homeless persons who abuse drugs and/or alcohol (Aim 1). Given the heterogeneity of the homeless population, in particular the ways in which the duration of homelessness can vary from a few nights to many years, the proposed research also seeks to determine whether factors associated with addiction treatment utilization differ according to the persistence of homelessness (Aim 2). The research program will use two existing datasets to address these aims. In Part 1, data from the 1996 National Survey of Homeless Assistance Providers and Clients will permit evaluation of factors associated with treatment utilization in a nationally representative cross-sectional survey of homeless persons. In Part 2, data from a completed 2-year prospective follow-up study of 470 homeless and housed persons addicted to drugs and/or alcohol will permit evaluation of factors associated with sustained treatment utilization, and evaluation of the relationship between treatment utilization and addiction outcomes. The value of treatment itself has been documented in the context of clinical trials. The importance of this proposed research lies in its potential to assist policymakers and treatment planners who wish to understand how to improve actual treatment access and treatment utilization by homeless persons who are addicted to drugs and/or alcohol. Career development activities for this career development award include the research itself, mentoring by individuals with extensive research experience in addiction and homelessness, and coursework to develop methodological expertise pertinent to the use of large and complex datasets, content expertise in the areas of addiction, addiction treatment theory, housing policy and homeless sociology, and research ethics. Completion of the proposed work will prepare Dr. Kertesz to independently investigate the treatment of drug and alcohol abuse in the homeless.